Studies On Temperature Effect Of Mechanical Properties And Micro Mechanism Of Rock Salt

Researching the effect of temperature on mechanical behavior for salt is the basis of analyzing and estimating security and stability for caverns in deep salt formation for natural gas storage, compression air energy storage and radioactive disposal. The previous many works were most focused on the effect on secondary creep rate. So far, the effects of temperature on damage, yield and plastical deformation of salt are not particularly researched. Additionally, engineering thermal analysis is important basic of management and stability analysis of cavern for natural gas storage, but studies on the engineering thermal analysis are not sufficient. The shape of the cavern is often assumed as cylinder or sphere. In some works, the engineering thermal analysis is based on the rigid container variable thermodynamics theory. Aiming at above problems, this dissertation analyzed the experiment outcome of salt heating tests and compression tests under different confining pressure and temperature, the micro-mechanism of deformation. For the engineering thermal analysis, the energy and the mass of the gas in cavern, the thermal field of the wall rock and the gas flowing in the well are also analyzed. The main research works of this dissertation are as follows:1. With the ultrasonic technology and spectrum analysis, the ultrasonic velocity, dynamical elastic parameters and the thermal damage evolution of rock salt under different temperature condition, including rising temperature and cycling temperature of different amplitude, are researched.2. Based on thermal damage mechanism for rock salt, effect of the material parameters, Young's modulus and linear expansion coefficient , on the thermal damage evolution is simulated. The effect of shape parameter(of Weibull distribution function) on thermal damage also analyzed by numerical simulation.3. The compaction-dilatancy boundaries(CDB) of Yingcheng Salt under different temperature are obtained form tri-axial compression datum and the modified CDB function also proposed. Based on the compaction-dilatancy theory for salt, sealability analysis of cavern for gas storage in salt formation by dilatancy approach index(DAI) is proposed, and the DAI definition and expression are also given. With the method, sealability of Jintan designed cavern is analyzed.4. The yield curves on p-q plane under different temperature are obtained with the tests for Yingcheng Salt. According to the micro-deformation mechanism, the yield stress of salt is analyzed and the yield stress function is introduced. Based on the equation, effect of temperature on the yield stress is analyzed.5. According to the composition theory and the dislocation and subgrain evolution of salt during the deformation, the plasticity constitutive model alt is made and the model is also validated by laboratory tests. Effect of temperature on plastical deformation of salt is analyzed by the proposed constitutive model.6. Based on the variable mass thermodynamics and former studies, engineering thermal analysis model for natural gas storage in deep salt formation and the solution of the model are presented. The presented model can be used for actual three dimension shape of the cavern and the thermal field of the salt formation. Engineering thermal analysis for Jintan single cavern during injection and production is simulated using the presented model and some results are concluded.